JPH0879315A - Optical signal deterioration detection circuit - Google Patents

Abstract

PURPOSE: To quicken the transfer of an optical signal deterioration alarm and to suppress the transmission of an undesired signal to a post-stage circuit and the effect of an warning by detecting missing of clock or frequency fluctuation caused at the initial stage of occurrence of deterioration in an optical signal. CONSTITUTION: A received optical signal 11 is converted into an electric signal by a light receiving element 12, and a transmission line clock signal 32 is extracted through a band-pass filter 17 and a limiter amplifier 31. The phase of the extracted transmission line clock signal 32 is compared with a phase of a reference clock signal 33 with a prescribed period by a phase comparator circuit 34. The deterioration in the optical signal is detected by the result of phase comparison. That is, an output fault of the transmission line clock signal is directly monitored by comparing a change in phase difference between the transmission line clock signal 32 and the reference clock signal 33. Since missing clock or fluctuation in the clock frequency of the transmission line clock signal 32 caused at the initial stage of the occurrence of deterioration in an optical signal is directly monitored, the optical deterioration state is detected early to quicken transfer of an alarm.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical signal deterioration detecting circuit for monitoring deterioration of an optical signal, for example, an optical signal deterioration detecting an optical signal deterioration occurring in a transition period leading to an optical input interruption and outputting an alarm. Regarding the detection circuit.

[0002]

2. Description of the Related Art In optical communication using a digital transmission system,
Generally, the transmitting side converts data into an optical signal together with a clock signal for synchronization and transmits the optical signal. In the receiver, the optical signal is converted into an electric signal, the clock signal is extracted, and the transmitted data is reproduced in synchronization with the clock signal. The clock signal that has passed through the transmission line is used as a timing signal for identifying and reproducing data, and is also used for timing signal processing of a circuit arranged in a stage subsequent to the optical receiving section. Therefore, if the optical signal is deteriorated, for example, the optical signal is interrupted and the clock signal cannot be normally extracted, not only the transmitted data is not normally reproduced,
There is a case where a failure such as the operation of the circuit arranged in the subsequent stage is stopped occurs. Therefore, the optical receiver of the optical receiver or the optical repeater is provided with an optical signal deterioration detection circuit for monitoring the extracted clock signal and detecting the deterioration of the optical signal.

Such an optical signal deterioration detecting circuit outputs an alarm when the deterioration of the optical signal is detected.
The occurrence of an alarm is monitored by an alarm monitoring device arranged in the optical communication system. When an alarm is detected, the action of switching to the backup line is taken. Alternatively, as described in JP-A-3-238939,
Simultaneously with the detection of the deterioration of the optical signal, a process of outputting the internal clock signal instead of the clock signal extracted from the transmission path is taken, and the occurrence of a failure in the circuit in the subsequent stage is avoided. As described above, the optical signal deterioration detection circuit protects the circuit arranged at the subsequent stage of the optical receiving unit from the spread of the failure. .

FIG. 9 shows the configuration of a conventional optical signal deterioration detection circuit. Optical signal 1 that has passed through the transmission path
1 is input to the light receiving element 12. The equivalent amplifier circuit 13 inputs the detection output 14 of the light receiving element 12 and amplifies it.
The automatic gain control circuit 15 is for controlling the voltage applied to the light receiving element 12 to make the output level of the output signal 16 of the equivalent amplification circuit 13 constant. The output signal 16 of the equivalent amplifier circuit 13 is branched and supplied to a not-shown discriminating and reproducing circuit and also to a bandpass filter 17. The bandpass filter 17 is an LC resonance circuit including a capacitor and a coil, and extracts the transmission path clock signal 18 from the output signal 16. The transmission line clock signal is a sine wave. This transmission path clock signal 18 is branched into two. One is input to an identification reproduction circuit (not shown) for identifying data via a limiter amplifier (not shown). The others are input to the full-wave rectifier 19. The full-wave rectifier 19 converts the transmission line clock signal 18 into a DC signal 20. Low pass filter 21
Receives this DC signal 20 and outputs a signal 22 representing its effective value. The potential of the signal 22 output from the low-pass filter 21 is changed by the comparator 23 to the reference potential 24.
Compared to. The input signal of the comparator 23 is the reference potential 24.
If it is smaller than this, a high level signal 25 is output. The high level signal 25 represents a deterioration warning of the optical signal.

An outline of the operation of such an optical signal deterioration detection circuit will be described. The digital optical signal 11 input to the light receiving element 12 is converted into an electric signal 14. Equivalent amplifier circuit 1
By amplifying the electric signal 14 at 3, a digital signal 16 corresponding to the digital optical signal 11 is obtained. The automatic gain control circuit 15 uses the digital signal 16
The voltage applied to the light receiving element 12 is controlled and the output level of the electric signal 14 is adjusted so that the output level of 1 is constant. The signal 16 output from the equivalent amplifier circuit 13 is input to the bandpass filter 17, and the transmission path clock signal 18
Is output as a sine wave. This transmission line clock signal 1
8 is converted into a DC signal 20 by the full-wave rectifier 14,
The low pass filter 21 outputs a signal representing the effective value of the transmission path clock signal.

When the optical signal 11 is normally input to the light receiving element 12, the automatic gain control circuit 15 makes the level of the signal 16 input to the bandpass filter 17 constant. That is, the extracted transmission line clock signal 18 is
It becomes a sine wave of equal amplitude. The signal 22 output from the low-pass filter 21 is a signal of a constant level that represents the effective value of this sine wave. The reference potential 24 is set smaller than the effective value signal in this case. Therefore, the comparator 23 outputs a low level signal.

On the other hand, it is assumed that the input intensity of the optical signal becomes low and exceeds the controllable range of the automatic gain control circuit 15. In this case, the output level of the signal input to the bandpass filter 17 becomes low. Therefore, the amplitude of the sine wave of the extracted transmission path clock signal also decreases, and the effective value of the transmission path clock signal output from the low-pass filter 21 decreases. In this way, when this value becomes smaller than the reference potential, the comparator 23 outputs a high level signal 25 indicating a light deterioration warning.

As described above, in the conventional optical signal deterioration detecting circuit, the deterioration of the input optical signal is detected by the effective value of the extracted transmission path clock signal.

Further, an improved optical signal deterioration detecting circuit having such a configuration is described in Japanese Patent Laid-Open No. 2-241236 and Japanese Utility Model Laid-Open No. 2-60351.

Japanese Unexamined Patent Publication No. 2-241236 is designed to prevent the optical signal deterioration warning from being erroneously sent out depending on the driving state of the automatic gain control circuit in the following specific cases. That is, when the intensity of the optical signal input to the light receiving element is large and the control by the automatic gain control circuit cannot follow, and the equivalent waveform is deteriorated, the error generated by the automatic gain control circuit is mistaken as the deterioration of the input optical signal. It prevents you from being judged.

Further, Japanese Utility Model Publication No. 2-60351 discloses that
A technique is disclosed in which a deterioration warning can be output even when the phase of a transmission path clock signal is disturbed. In this proposal, the jitter detection circuit for monitoring the phase disturbance of the extracted transmission path clock signal is arranged in the preceding stage of the full-wave rectifier for detecting the effective value of the transmission path clock signal shown in FIG. . The jitter detection circuit outputs a level signal lower than a predetermined level signal in response to the disturbance when the phase of the extracted transmission path clock signal is disturbed. As a result, the deterioration due to the phase fluctuation of the input optical signal is converted into a decrease in the output level of the transmission path clock signal and is output as a deterioration warning.

[0012]

Deterioration of an optical signal often occurs through a transient state in which a normal state and a state of deterioration are repeated, rather than a case where the optical signal usually occurs instantaneously. For example, even if the optical input is disconnected due to mechanical damage to the optical fiber, the optical input is rarely instantaneously compared with the repetition period of the clock signal. Usually, clock dropouts and frequency fluctuations occur intermittently. Therefore, if the deterioration of the optical signal can be detected early before the optical signal is constantly deteriorated, it is possible to minimize the trouble occurring in the subsequent circuit.

However, in the above-described conventional optical signal deterioration detecting circuit, since the deterioration of the optical signal is detected from the average value of the output level of the transmission path clock signal, the deterioration occurs intermittently during the transition period of the deterioration. It was difficult to detect the deterioration of the optical signal. That is, since the deterioration of the input optical signal is detected by analog processing, the followability to the intermittent deterioration of the optical signal is poor, and the initial state of the deterioration of the optical signal cannot be detected. Therefore, there is a problem that a time delay occurs from the occurrence of the deterioration of the optical signal to the sending of the alarm.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an optical signal deterioration detecting circuit which can speed up the detection of the deterioration state of an optical signal and prevent the propagation of a failure to a subsequent circuit.

[0015]

According to a first aspect of the invention, (a) an opto-electric conversion means for converting a transmitted optical signal into an electric signal, and (b) an electric power converted by the opto-electric conversion means. A transmission path clock pulse extracting means for extracting a transmission path clock pulse transmitted from the signal;
Reference clock pulse output means for outputting a reference clock pulse having a predetermined constant period, and (d) the reference clock pulse output from the reference clock pulse output means and the transmission path clock pulse extracted by the transmission path clock pulse extraction means. And the phase comparison means for comparing these phases to detect the amount of change in the phase shift, and (e) the light when the amount of change in the phase shift detected by the phase comparison means is larger than a predetermined reference value. An optical signal deterioration detecting circuit is provided with an optical signal deterioration detecting means for detecting signal deterioration.

That is, according to the first aspect of the invention, after converting the transmitted optical signal into an electric signal, the transmission path clock pulse is extracted. The extracted transmission path clock pulse is compared in phase with a reference clock pulse having a predetermined constant period. From this comparison result, it is detected that the optical signal is deteriorated when the change amount of the phase shift is large. That is, since the abnormality of the output of the transmission path clock pulse is directly monitored by comparing the phases of the transmission path clock pulse and the reference clock pulse, it is possible to accelerate the detection of the optical deterioration.

According to a second aspect of the invention, (a) an opto-electric conversion means for converting the transmitted optical signal into an electric signal,
(B) Transmission path clock pulse extraction means for extracting transmission path clock pulses transmitted from the electrical signal converted by the opto-electric conversion means; and (c) transmission path clock pulse extracted by the transmission path clock pulse extraction means. Counting means for counting, and (d) reference clock pulse output means for outputting a reference clock pulse having a predetermined constant period longer than the repetition period of the transmission path clock pulse extracted by the transmission path clock pulse extraction means,
(E) Initializing means for initializing the count value of the counting means each time a reference clock pulse is output from the reference clock pulse output means, and (e) counting between initialization by the initializing means. Comparing means for comparing a predetermined value as the number of transmission path clock pulses with a value counted by the counting means, and (g) the count value of the counting means by the comparing means is smaller than the predetermined value. The optical signal deterioration detection circuit is provided with an optical deterioration alarm output means for outputting an optical deterioration alarm when it is detected.

That is, according to the second aspect of the invention, the counting means counts the transmission path clock pulses. Every time the reference clock pulse is output, the count value is initialized. The count value is monitored, and when it is smaller than a predetermined value, it is detected and a photodegradation signal is output. Therefore, since the abnormality of the output of the transmission path clock pulse is directly monitored, the alarm can be transferred more quickly.

According to a third aspect of the invention, (a) an opto-electric conversion means for converting the transmitted optical signal into an electric signal,
(B) Transmission path clock pulse extraction means for extracting transmission path clock pulses transmitted from the electrical signal converted by the opto-electric conversion means; and (c) transmission path clock pulse extracted by the transmission path clock pulse extraction means. Counting means, (d) a reference clock pulse output means for outputting a reference clock pulse of a predetermined cycle that can be determined in advance, and (e) a time point at which the reference clock pulse is output from the reference clock pulse output means. Initializing means for initializing the count value of the counting means by (6), and (f) a predetermined value as the number of transmission path clock pulses counted until the initialization by the initializing means and the counting means Comparing means for comparing the
(G) The optical signal deterioration detection circuit is provided with an optical deterioration alarm output unit that outputs an optical deterioration alarm when the comparison unit detects that the count value of the counting unit is smaller than a predetermined value.

That is, according to the third aspect of the invention, the counting means counts the transmission path clock pulses, and the count value is initialized when the clock pulse of the reference clock signal whose frequency can be arbitrarily changed arrives. . The count value is monitored, and when it is smaller than a predetermined value that can be arbitrarily changed, a photodegradation signal is output. Therefore, the condition for determining the deterioration of the optical signal can be changed as necessary, so that monitoring can be performed according to the occurrence state of the deterioration, and the deterioration can be detected earlier.

According to a fourth aspect of the invention, (a) an opto-electric conversion means for converting the transmitted optical signal into an electric signal,
(B) Transmission path clock pulse extraction means for extracting transmission path clock pulses transmitted from the electrical signal converted by the opto-electric conversion means; and (c) transmission path clock pulse extracted by the transmission path clock pulse extraction means. A plurality of counting means for counting, and (d) reference clock pulse output means for outputting a reference clock pulse having a repeating period longer than the repeating period of the transmission path clock pulse extracted by the transmission path clock pulse extracting means,
(E) Phase conversion means for changing the phase of the reference clock pulse output from the reference clock pulse output means to input the reference clock pulses of different phases to the plurality of counting means, and (f) the clock signal from the phase conversion means. Is initialized as the number of the transmission path clock pulses counted before the initialization by the initialization means and (g) the initialization means. A photo-deterioration alarm when it is detected by any one of the comparison means for comparing the value and the value counted by the counting means, and (h) the comparing means, that the count value of the counting means is smaller than a predetermined value. The optical signal deterioration detection circuit is provided with an optical deterioration alarm output means for outputting.

That is, in the invention according to the fourth aspect, a plurality of counting means are provided and the transmission path clock pulses are counted complementarily to each other during the repeating cycle of the reference clock pulse. Therefore, the alarm signal can be transferred more quickly.

According to a fifth aspect of the invention, (a) an opto-electric conversion means for converting the transmitted optical signal into an electric signal,
(B) Transmission path clock pulse extraction means for extracting the transmission path clock pulse transmitted from the electric signal converted by the photoelectric conversion means, and (c) a reference for outputting a reference clock pulse of a predetermined constant period. Of the repetition cycle of the reference clock pulse by inputting the clock pulse output means, the reference clock pulse output from the reference clock pulse output means (d) and the transmission path clock pulse extracted by the transmission path clock pulse output means. The optical signal deterioration detection circuit is provided with an optical signal deterioration warning output means for outputting an optical signal deterioration warning when the transmission path clock pulse does not arrive within the specified constant period.

That is, according to the fifth aspect of the invention, it is detected whether or not the transmission path clock pulse is present during the repetition period of the reference clock pulse. Since the presence or absence of a clock is directly monitored, the alarm can be transferred quickly.

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to embodiments.

FIG. 1 shows in principle the configuration of an optical signal deterioration detection circuit according to an embodiment of the present invention. Figure 9
The same components as those of the above are denoted by the same reference numerals, and the description thereof will be appropriately omitted. The optical signal 11 transmitted through a transmission line (not shown) is converted into an electric signal 14 by the light receiving element 12, equivalently amplified by the equivalent amplifier circuit 13, and then input to the bandpass filter 17. The transmission path clock signal 18 extracted by the bandpass filter 12 is waveform-shaped by the limiter amplifier 31.
The waveform-shaped transmission path clock signal 32 is branched into two, and one is input to an identification reproduction circuit (not shown) for identifying and reproducing the transmitted signal. The others are input to the phase comparison circuit 34 which compares the phase with the reference clock signal 33. The reference clock signal 33 is a clock signal having a specific cycle. This is an adjustment of a signal output from an oscillator peculiar to the device, which is used for the timing of driving a circuit in the subsequent stage (not shown). The phase comparison circuit 34 outputs the phase comparison 35.

FIG. 2 specifically shows the circuit configuration of the phase comparison circuit in the optical signal deterioration detection circuit of this embodiment. The transmission path clock signal 32 is input to the counter 41. The counter 41 is for counting the transmission path clock signal 32. Counter 4
The reference clock signal 33 is input to the terminal 1 as a load signal. The counter 41 is loaded with "0" as an initial value every time the reference clock signal 33 rises. This counter 41 is 2 of 4
It is possible to count up to the power, and the counted value 43 is output to the latch circuit 44 as a parallel 4-bit digital signal. The latch circuit 44 holds the count value of the counter 41 when the reference clock signal 33 rises. The output signal 45 of the latch circuit 44 is input to the comparison circuit 46. In the comparison circuit 46, the preset reference signal 47 and the latch circuit 44 are set.
The output signals 45 of the above are compared. When the count value is smaller than the reference value represented by the reference signal 47, the signal 35 is set to the high level. The high level signal 35 represents a light deterioration warning. When the signal 35 is at a low level, it means that the signal is normal.

First, the operation when a normal transmission path clock signal is input to the optical signal deterioration detection circuit having such a configuration will be described.

FIG. 3 shows the waveform of each part of the phase comparison circuit when the transmission path clock signal is normally extracted. Transmission line clock signal 32 (a in the figure)
Are input to the counter 41 at regular intervals. The reference clock signal 33 (b in the figure) is also input at a constant cycle. In this embodiment, the cycle of the reference clock signal 33 is set to about 6 times that of the transmission line clock signal 32. The count value 43 of the counter 41 is reset to "0" when the reference clock signal 33 rises. After that, the count value 43 of the counter 41 is sequentially incremented from "1" in accordance with the transmission path clock signal 34 (FIG. 7C). When the reference clock signal 33 rises next, the count value 43 of the counter 41 is held in the latch circuit 44. The count value at this time is "6". At this time, the counter 41 is reset again and the count value returns to "0". Since the cycle of the reference clock signal is constant, the count value of the counter 41 also becomes "6" at the time when the next reference clock signal arrives. In this way, the latch circuit 44 holds the count value of the transmission path clock signal 32 one after another every time the reference clock signal 33 rises.

The comparator circuit 46 counts "6" held by the latch circuit 44 each time the reference clock signal rises.
And a predetermined reference value “5” are compared. Since the count value is larger than the reference value, the signal 35 output from the comparison circuit 46 becomes low level, and the alarm is not transferred. The reference value is set depending on how much the clock count or frequency fluctuation is judged to be deterioration from the value that can be counted during normal operation. In the present embodiment, it is assumed that 1 to 2 clock omissions are not considered to be deterioration, and is set to a value "5" that is one less than the value "6" that is normally counted.

Next, the operation of the optical signal deterioration detection circuit when the extracted transmission path clock signal is deteriorated will be described.

When the optical signal deteriorates, in the transient state due to the deterioration, a phenomenon of clock omission or clock frequency fluctuation occurs in the extracted transmission line clock signal.

FIG. 4 shows the waveform of each part of the phase comparison circuit when the extracted transmission line clock signal is deteriorated. When the time T ₁₁ dislodgement line clock signal between the through T ₁₂ occurs, the counter does not count up during this time. The count value is held until the next clock signal is input at time T ₁₂ . Therefore, the reference clock signal next rises, and the value held by the latch circuit 44 becomes smaller than that in the normal state and becomes "3" (FIG. 7C).

Similarly, when the clock frequency fluctuates after the time T ₁₃ , the count-up interval of the counter changes according to the clock frequency fluctuation. Therefore, the value counted until the clock pulse of the reference clock signal arrives again becomes small and becomes "4".

As described above, when a clock dropout or clock frequency fluctuation occurs, the digital signal representing the count value of the counter input to the comparison circuit is the reference value "5".
Will be smaller than. Therefore, the output signal 35 of the comparison circuit 46 becomes high level, and the deterioration alarm is transferred. By counting the transmission path clock signals in this way, it is possible to detect deterioration of the optical signal such as clock omissions and frequency fluctuations.

In the above-mentioned embodiment, the output of the counter is 4 bits, but the output is not limited to this. Further, the repetition cycle of the reference clock signal is set to about 6 times that of the transmission path clock signal, but it is not limited to this. If the cycle of the reference clock can be arbitrarily changed, the deterioration determination condition of the optical signal can be changed as necessary, and the deterioration state can be individually and quickly detected. At this time, since the reference clock signal and the transmission path clock signal are asynchronous, the count value of the latch circuit changes slightly even in a normal state. Therefore, it is necessary to take this into consideration when setting the reference value. .

Modification

FIG. 5 shows a circuit configuration of a phase comparison circuit according to a modification of the present invention. Two counters, a first counter 41 ₁ and a second counter 41 ₂ are prepared inside the phase comparison circuit to count the transmission path clock signal 34. The first counter 41 ₁ is initialized when the reference clock signal 33 rises. An inverted reference clock signal 52, the phase of which is inverted by the inversion circuit 51, is input to the second counter 41 ₂ . Therefore, the second counter 41 ₂ is initialized later than the first counter 41 ₁ by a half cycle of the reference clock signal 33. The values counted by the first counter and the second counter are respectively the reference clock signal 36
And when the inverted reference clock signal 52 rises, it is held by the first latch circuit 44 ₁ and the second latch circuit 44 ₂ . These values are input to the first comparison circuit 46 ₁ and the second comparison circuit 46 ₂ , respectively, and the reference value 47
Compared with ₁ , 47 ₂ . First and second comparison circuit 4
In 6 ₁ and 46 ₂ , when the count value is smaller than the reference value, the signals 48 ₁ and 48 ₂ are set to the high level and output. These signals are input to the OR circuit 53. First comparison circuit 46 ₁ or second comparison circuit 46 ₂
When a high level signal is output by any of the above, the output signal 35 of the OR circuit 53 becomes a high level and the alarm information is transferred.

By adopting such a configuration, it is possible to detect the deterioration early at an interval of ½ of the repetition period of the reference clock signal without changing the criterion for judging the deterioration of the optical signal.

Second embodiment

In the above embodiment, the counter monitors the number of clocks of the transmission path clock signal to monitor the deterioration of the optical signal and output an alarm. The deterioration of the clock loss can be determined by whether or not the transmission path clock signal is included within a certain period.

FIG. 6 shows the configuration of the phase comparison circuit of the optical signal deterioration detection circuit according to the second embodiment.
The first to third flip-flop circuits 61 to 63 are connected in cascade. The transmission line clock signal 32 output from the limiter amplifier 31 of FIG. 1 is input from the reset terminals of the first to third flip-flop circuits 61 to 63, respectively. The reference clock signal 33 is the first
~ Input is made from the clock terminal of the third flip-flop circuit. First flip-flop circuit 3
The signal 64 is input to the 1 input terminal in a high level state. The output terminal of the first flip-flop circuit 61 is connected to the input terminal of the second flip-flop circuit 62, and the output terminal of the second flip-flop circuit 62 is the third terminal.
Of the flip-flop circuit 63.

First, the operation in the case where a normal transmission path clock signal is input to the optical signal deterioration detection circuit having such a configuration will be described.

FIG. 7 shows a waveform input to the optical signal deterioration detection circuit when the transmission path clock signal is normally extracted. Transmission line clock signal 33
(A) in the figure shows the first to third flip-flop circuits 61 to 61.
Input from the reset terminal 63. While the transmission line clock signal 32 is at the high level, the potentials on the output terminal side of the first and second flip-flop circuits 61 and 62 are reset. The repeating cycle of the reference clock signal 33 (b in the figure) is made slightly longer than the repeating cycle of the transmission path clock signal 32. Therefore, even when the potential between the first and second flip-flop circuits is transferred to the first flip-flop circuit 61 and is at the high level, the first flip-flop circuit before the new reference clock signal 33 rises. It is always reset by the circuit 61 and becomes low level. Therefore, the high-level signal 64 input to the first flip-flop circuit 61 is not transferred to the output side of the second flip-flop circuit 62, and the output signal of the third flip-flop circuit 63 becomes high-level. There is no.

Next, the operation when the transmission line clock signal is deteriorated will be described.

FIG. 8 shows a signal waveform input to the optical signal deterioration detection circuit when the transmission path clock signal is not normally extracted. It is assumed that the transmission path extraction clock signal 32 (a in the figure) has a missing clock between time T ₂₁ and time T ₂₂ . In this case, the high level of the signal 64 inputted from the input terminal of the first flip-flop circuit 61 at time T ₂₃ is transferred to the output terminal side. The potential between the first and second flip-flop circuits is kept until the next rising time T ₂₄ of the reference clock signal,
Since it is not reset by the transmission path clock signal 32, it is kept at the high level. Then, at time T ₂₄ when the reference clock signal next rises, the high-level potential is output by the second flip-flop circuit 62 to the input side of the third flip-flop circuit 63. Similarly, the potential between the second and third flip-flop circuits also remains at the high level because the transmission path clock signal does not rise between time T ₂₄ and time T ₂₅ and is not reset by the second flip-flop circuit 62. Retained. Then, when the reference clock signal next rises, the output of the third flip-flop circuit 63 becomes high level. In this way, a high-level signal that is not normally sent is sent, which gives an alarm indicating that optical deterioration has occurred.

In the second embodiment, the deterioration warning signal 3 is generated when the clock pulse dropout of the transmission path clock signal for two cycles of the reference clock repetition cycle occurs in this way.
5 was set to be transmitted. However, by changing the number of stages of the flip-flop circuit or the repetition cycle of the reference clock, the discrimination condition for photodegradation can be freely changed.

[0048]

As described above, according to the first aspect of the invention, the output abnormality of the transmission line clock signal is directly monitored by comparing the phases of the transmission line clock signal and the reference clock signal with respect to the optical signal deterioration. Therefore, the detection of light deterioration can be accelerated. The clock loss and clock frequency fluctuations that occur in the transient state are detected by the phase comparison circuit and output as an optical signal deterioration alarm. Therefore, in the circuit in the subsequent stage, the time from the deterioration of the optical signal to the detection of the alarm can be shortened as compared with the conventional case, so that the transfer of unnecessary signals can be suppressed and the occurrence of trouble can be suppressed.

Further, according to the second aspect of the invention, since the deterioration of the optical signal is detected by counting the transmission path clock signals for each specific cycle, the clock omission or the frequency fluctuation which occurs at the early stage of the deterioration occurrence. Even the intermittent deterioration of the optical signal can be detected.

Further, according to the third aspect of the present invention, since the period for monitoring the deterioration of the optical signal can be arbitrarily changed, when the deterioration state of the optical signal, for example, there is a lot of clock loss,
Alternatively, it is possible to detect the deterioration of the optical signal at an early stage depending on the case where the frequency variation is large.

According to the fourth aspect of the invention, since the plurality of counting means count the transmission path clock signals by providing time differences respectively, the condition for determining the deterioration of the optical signal is not changed. Moreover, the time required for detecting the deterioration of the optical signal can be further shortened.

Further, according to the invention of claim 5, the presence or absence of a pulse of the transmission path clock signal is monitored within a predetermined period and the deterioration of the optical signal is detected.
Deterioration of optical signals can be detected.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing in principle the configuration of an optical signal deterioration detection circuit according to an embodiment of the present invention.

FIG. 2 is a circuit diagram specifically showing a circuit configuration of a main part of an optical signal deterioration detection circuit of this embodiment.

FIG. 3 is a timing chart showing the signal waveform of each part of the optical signal deterioration detection circuit in the normal state of the transmission path clock signal in the present embodiment.

FIG. 4 is a timing chart showing signal waveforms of respective parts of the optical signal deterioration detection circuit in a state where the transmission path clock signal is deteriorated in the present embodiment.

FIG. 5 is a circuit diagram specifically showing a circuit configuration of a main part of an optical signal deterioration detection circuit in a modified example of the present invention.

FIG. 6 is a circuit diagram showing a configuration of a phase comparison circuit of an optical signal deterioration detection circuit according to a second embodiment.

FIG. 7 is a waveform diagram showing a signal waveform of each part of the optical signal deterioration detection circuit in a normal state of the transmission path clock signal in the second embodiment.

FIG. 8 is a waveform diagram showing signal waveforms of respective parts of the optical signal deterioration detection circuit in a state where the transmission path clock signal is deteriorated in the second embodiment.

FIG. 9 is a circuit diagram showing a configuration of an optical receiving circuit including a conventional general optical signal monitoring circuit.

[Explanation of symbols]

 11 Optical Signal 17 Band Pass Filter 31 Limiter Amplifier 32 Transmission Line Clock Signal 33 Reference Clock Pulse 34 Phase Comparison Circuit 35 Optical Degradation Warning 41 Counter 44 Latch Circuit 46 Comparison Circuit 53 OR Circuit 61-63 Flip-Flop Circuit

Claims (5)

[Claims] 1. A photoelectric conversion means for converting a transmitted optical signal into an electric signal, and a transmission path clock pulse for extracting a transmission path clock pulse transmitted from the electric signal converted by the photoelectric conversion means. Extraction means, reference clock pulse output means for outputting a reference clock pulse of a predetermined constant cycle, reference clock pulse output from the reference clock pulse output means, and transmission extracted by the transmission path clock pulse output means A phase comparison means for inputting a road clock pulse and comparing these phases to detect the amount of change in the phase deviation, and when the amount of change in the phase deviation detected by the phase comparison means is larger than a predetermined reference value. An optical signal deterioration detecting circuit, comprising: an optical signal deterioration detecting means for detecting deterioration of an optical signal. 2. A photoelectric conversion means for converting the transmitted optical signal into an electric signal, and a transmission path clock pulse for extracting the transmission path clock pulse transmitted from the electric signal converted by the photoelectric conversion means. Extraction means, counting means for counting the transmission path clock pulses extracted by the transmission path clock pulse extraction means, and a predetermined period longer than the repetition cycle of the transmission path clock pulses extracted by the transmission path clock pulse extraction means A reference clock pulse output means for outputting a reference clock pulse having a constant period, and an initialization means for initializing the count value of the counting means at each time when the reference clock pulse is output from the reference clock pulse output means, Transmission path clock pulse counted until it is initialized by this initialization means. Comparing means for comparing a value predetermined by the counting means with the value counted by the counting means, and when it is detected by the comparing means that the count value of the counting means is smaller than the predetermined value. An optical signal deterioration detection circuit, comprising: an optical signal deterioration alarm output means for outputting an optical signal deterioration alarm. 3. A photoelectric conversion means for converting the transmitted optical signal into an electric signal, and a transmission path clock pulse for extracting the transmission path clock pulse transmitted from the electric signal converted by the photoelectric conversion means. Extraction means, counting means for counting the transmission path clock pulses extracted by the transmission path clock pulse extraction means, reference clock pulse output means for outputting a reference clock pulse of a predetermined fixed cycle, and this reference clock Initializing means for initializing the count value of the counting means each time a reference clock pulse is output from the pulse output means, and a transmission path clock pulse counted before being initialized by the initializing means Comparing means for comparing a value determined by the counting means with a value predetermined as the number of An optical signal deterioration warning output means for outputting an optical signal deterioration warning when the comparison means detects that the count value of the counting means is smaller than a predetermined value. circuit. 4. A photoelectric conversion means for converting the transmitted optical signal into an electric signal, and a transmission line clock pulse for extracting a transmission line clock pulse transmitted from the electric signal converted by the photoelectric conversion means. Extracting means, a plurality of counting means for counting the transmission path clock pulses extracted by the transmission path clock pulse extracting means, and a repetition longer than the repetition cycle of the transmission path clock pulses extracted by the transmission path clock pulse extracting means Reference clock pulse output means for outputting a reference clock pulse having a cycle, and a phase of the reference clock pulse output from the reference clock pulse output means is changed to input reference clock pulses of different phases to the plurality of counting means. And a reference clock from this phase conversion means. Initialization means for initializing the count value of the counting means each time a pulse is output, and a predetermined number of transmission path clock pulses counted until the initialization by the initialization means. Comparing means for comparing the value with the value counted by the counting means, and an optical signal deterioration alarm when it is detected by any one of the comparing means that the count value of the counting means is smaller than a predetermined value And an optical signal deterioration warning output means for outputting the optical signal deterioration detection circuit. 5. An opto-electric conversion means for converting the transmitted optical signal into an electric signal, and a transmission path clock extraction for extracting a transmission path clock pulse transmitted from the electric signal converted by the opto-electric conversion means. Means, a reference clock pulse output means for outputting a reference clock pulse of a predetermined constant cycle, a reference clock pulse output from the reference clock pulse output means, and a transmission path extracted by the transmission path clock pulse output means An optical signal deterioration warning output means for inputting a clock pulse and outputting an optical signal deterioration warning when a transmission path clock pulse does not arrive within a specified fixed cycle of the reference clock pulse repetition cycle. An optical signal deterioration detection circuit characterized by: